1. Field of the Invention
This invention relates to the optical stabilization of images provided the recording surface of a hand-held video or film camera. More particularly, the invention relates to an optically stabilized zoom lens suitable for use with conventional hand-held cameras in lieu of conventional removable zoom lens.
2. Summary of the Prior Art
Stabilized optics using a reflecting and displacing prism, disclosed in U.S. Pat. No. 3,475,073, issued on Oct. 28, 1969 to William E. Humphrey, are known. The prism disclosed in this patent, hereinafter sometimes referred to as the Humphrey prism, provides optical stabilization against certain types of inadvertent movements of the instrument. This optical stabilization is achieved by the Humphrey prism, when used with an objective lens system, providing a stabilized image at a fixed location relative to the lens case. The Humphrey patent also discloses other reflecting and displacing optical elements, for example one using three mirrors, which together with the Humphrey prism are hereinafter collectively referred to as Humphrey-type optical elements.
Because of this stabilization property, Humphrey prisms have been used in gyroscopically stabilized optical devices. For example, one such device has been sold by Mark Systems of Cupertino, Calif. under the trademark MARK 1610. This device, which is a mono-binocular, uses a two degree of freedom gyroscope, commonly referred to as a Cardan suspension, to support the prism. This type of suspension, in which the prism is rigidly secured to one of the gimbals, helps to stabilize the viewer's image since small movements of the mono-binocular case will not affect the gyrostabilized prism. Although this instrument provides a stabilized image for the viewer, the resultant image is subject to high frequency vibrations, such as those produced by the spinning rotor of the gyroscope. The Humphrey U.S. Pat. No. 3,475,023 patent acknowledges the zoom lens assemblies and relay optics may be used with the prism stabilizing scheme therein disclosed. It does not disclose how such systems are optimized for practical use. Indeed, despite attempts to utilize these technology in the past, commercial success has not been achieved.
Devices that can stabilize the line of sight of an ordinary motion picture or video camera by stabilizing the camera itself have been in use for many years. These devices may employ either a gyro system or a greatly increased moment of inertia to accomplish such stabilization. For mechanical reasons such systems are large, heavy and expensive, and are therefore most often rented for special occasions, such as the production of documentaries, commercials, etc., where the picture-making can be scheduled at some predetermined and schedulable time in the future.
Electronic news gathering (ENG) is an increasingly important segment of the television industry. Even a casual review of a single week of TV national network newscasts will convince the viewer that fast-breaking news reporting of such events as airplane hi-jackings, riots, accidents, natural disasters and other such scenes shot from helicopters, while in a moving car, etc., do not have the benefit of image stabilization. If the TV networks were offered footage of ordinary news events with such glaring technical defects, they would reject them as being hopelessly amateurish. But because of their newsworthiness, these very unsteady shots are shown in spite of their obvious technical faults.